The present invention relates to novel aryl- or aralkylbenzenes having two benzene rings at least one of which is substituted by at least one 3,3,3-trifluoropropyl group and also to a novel process for producing them. The aryl- or aralkylbenzene having two benzene rings at least one of which is substituted by at least one 3,3,3-trifluoropropyl group is expected to be, for example, dielectric materials.
As a means for synthesizing such an aromatic compounds having benzene ring substituted by 3,3,3-trifluoropropyl group, only one process has been proposed (U.S. Pat. No. 3,080,428), in which 3,3,3-trifluoropropyl ether, (CF.sub.3 CH.sub.2 CH.sub.2).sub.2 O, is brought into reaction with benzene in the presence of hydrogen fluoride to obtain (3,3,3-trifluoropropyl)benzene. However, since in the above-mentioned process, water is formed by the reaction, the activity of the catalyst is reduced during the reaction, and the recovery of once-used catalyst is difficult. Moreover, 3,3,3-trifluoropropyl ehter as the starting material is synthesized by the reaction of hydrogen fluoride, formaldehyde (or its polymer) and vinylidene fluoride. Accordingly, 3,3,3-trifluoropropyl ether is expensive because of the high price of vinylidene fluoride and of the yield of synthesizing the ether as low as 50 to 60%.
It is an object of the present invention to provide a trifluoropropyl derivative of aryl-or aralkylbenzene of the general formula: ##STR2## wherein R is a not-substituted or substituted phenyl group, benzyl group, phenethyl group or alpha-methylbenzyl group by 3,3,3-trifluoropropyl group and n is 1, 2 or 3, provided that the total number of 3,3,3-trifluoropropyl group in said trifluoropropyl derivative of aryl- or aralkylbenzene is at most 3. A further object is to provide a process for producing an aryl- or aralkylbenzene having at least one benzene ring substituted by at least one 3,3,3-trifluoropropyl group, which comprises bringing an aryl- or aralkylbenzene of the formula ##STR3## wherein R.sup.1 represents phenyl group, benzyl group, phenethyl group or alpha-methylbenzyl group, into reaction with 3,3,3-trifluoropropylene in the presence of an acid catalyst, such as hydrogen fluoride or boron trifluoride. In addition, the reaction between biphenyl and 3,3,3-trifluoropropylene may also be carried out in the presence of a mixture of hydrogen fluoride and boron trifluoride as the catalyst.
Other object is to provide an dielectric material comprising at least one of 3,3,3-trifluoropropyl derivative of aryl- or aralkylbenzene. Another object is to provide a substituted aryl- or aralkylbenzene by 3,3,3-trifluoropropyl group obtained by bringing aryl- or aralkylbenzene into reaction with 3,3,3-trifluoropropylene in the presence of an acid catalyst, and separating said substituted aryl- or aralkylbenzene from the resultant reaction mixture. Still other objects and advantages of the present invention will become apparent hereinafter.
In the Drawing, FIGS. 1 and 2 show the infrared absorption spectrum and the mass spectrum, respectively of (3,3,3-trifluoropropyl)biphenyl; FIGS. 3 and 4 show those, respectively of biphenyl di-substituted by 3,3,3-trifluoropropyl groups; FIGS. 5 and 6 show those, respectively of diphenylmethane mono-substituted by 3,3,3-trifluoropropyl group; FIGS. 7 and 8 show those, respectively of 1,2-diphenylethane mono-substituted by 3,3,3-trifluoropropyl group; FIGS. 9 and 10 show those, respectively of 1,2-diphenylethane di-substituted by 3,3,3-trifluoropropyl groups and FIGS. 11 and 12 show those, respectively of 1,1-diphenylethane mono-substituted by 3,3,3-trifluoropropyl group.
Th aryl- or aralkylbenzenes having two benzene rings at least one of which is substituted by at least one 3,3,3-trifluoropropyl group according to the present invention are novel chemical compounds and will be used for a variety of purposes.
Furthermore, the above-mentioned mono-substituted aryl- or aralkylbenzene by 3,3,3-trifluoropropyl group according to the present invention are desirably biodegradable.
The concrete examples of synthesis of the novel trifluoropropyl derivatives of the present invention are described in Table 1, however, the syntheses of such derivatives are not confined therein.
TABLE 1 __________________________________________________________________________ Examples of synthesizing the trifluoropropyl derivatives of arylbenzene or aralkylbenzene of the present invention __________________________________________________________________________ [A] ##STR4## (I) [B] ##STR5## (II) [C] ##STR6## (III) wherein (i) a = 0 and b = 2, or (ii) a = b = 1 in the reaction formula (II); (ii) c = 0 and d = 3, or (iv) c = 1 and d = 2 in the reaction formula (III); and further X means (A) a direct bonding between the two benzene rings namely the parent compound being diphenyl, (B) a methylene group, i.e., CH.sub.2, namely the parent compound being diphenyl- methane. (C) an ethylene group, i.e., CH.sub.2CH.sub.2, namely the parent compound being 1,2-diphenylethane, or (D) ##STR7## In addition, there is a reaction giving the same product as in (I) wherein X is a methylene group, as follows: [D] ##STR8## __________________________________________________________________________
Since the trifluoropropyl derivatives of the present invention are excellent in electric properties, such as insulating property and dielectric property, they are possibly utilized as an insulating oil such as the insulating oil in capacitor, the above-mentioned specific properties of the derivatives of the present invention being presumed due to its trifluoropropyl group.
The process for synthesizing the compound of the present invention is described as follows: Generally, the compound of the present invention is synthesized by bringing the corresponding aromatic compound into reaction with 3,3,3-trifluoropropylene in the presence of an acid catalyst.
In the afore-mentioned reactions, since 3,3,3-trifluoropropylene (CF.sub.3 -CH.dbd.CH.sub.2) used in the present invention has a strongly electron-withdrawing group, -CF.sub.3, the basicity of the C-C double bond within the molecule of 3,3,3-trifluoropropylene is weaker than the basicity of the non-substituted parent compound, propylene (CH.sub.3 -CH.dbd.CH.sub.2). Accordingly, in the reaction of 3,3,3-trifluoropropylene and an aromatic compound such as aryl- or aralkylbenzene, the presence of a strongly acidic Friedel-Crafts catalyst is necesary. However, in the case where one of the representative Friedel-Crafts catalyst, for example, anhydrous alminum chloride is used, substitution of aromatic ring by chlorine atom and cyclization of the starting material are caused by the catalyst. On the other hand, anhydrous ferric chloride which is weaker than anhydrous aluminum chloride is almost inactive in the present reaction. Even if a silica-alumina catalyst is used, the desired compound is available only in a poor yield because of the occurence of various side reactions.
As a result of keen efforts of finding the appropriate catalyst for smoothly carrying out the present reaction, the inventors of the present invention have found out that hydrogen fluoride, boron trifluoride and a mixture thereof are effective in the present reaction. Since the catalyst for use in the present invention is a gas in normal state or a low-boiling liquid, the removal of the catalyst after ending the reaction is simply effected by stripping, and accordingly, the recovery and the reuse of the recovered catalyst are easily performed. In practicizing the process of the present invention, the catalyst is preferably used in an amount of more than 0.5 mole per mole of the aromatic compound as the starting material.
The reaction temperature depends upon the species of the startng material and the catalyst, and from the viewpoint of the species and activity of the catalyst, the temperature at which a catalyst shows its activity is highest in the case of hydrogen fluoride followed by boron trifluoride and then by mixtures of hydrogen fluoride and boron trifluoride.
Among the aromatic compounds used in the present invention as the starting material, although biphenyl is relatively stable in the reaction system of the process of the present invention, diphenylmethane and diphenylethanes may be decomposed in some cases where the reaction conditions are severe enough. Accordingly, the suitable reaction temperature depends upon the species of the starting material and the catalyst, and the preferable reaction temperature is, for example, -20.degree. to 100.degree. C. in the case of a mixture of hydrogen fluoride and boron trifluoride, 0.degree. to 120.degree. C. in the case of boron trifluoride and 50.degree. and 150.degree. C. in the case of hydrogen fluoride as the catalyst. At such a reaction temperature, the reaction completes within one to 30 hours.
While the product of the present reaction between propylene and an aromatic compound is an aromatic compound substituted by isopropyl group, (CH.sub.3).sub.2 CH-, the product of the present reaction between 3,3,3-trifluoropropylene and an aromatic compound is an aromatic compound substituted by 3,3,3-trifluoropropyl group, CF.sub.3 CH.sub.2 CH.sub.2 -, this fact having been confirmed by .sup.1 H-NMR- and .sup.19 F-NMR spectra.
After the reaction is over, the unreacted gas is purged and the remained catalyst is removed by means of stripping, neutralizing or washing, and the reaction product is obtained by distillation under reduced pressure.
In the last-mentioned reaction in Table 1: ##STR9## the starting material used in the afore-mentioned reaction, (3,3,3-trifluoropropyl)benzene is, as has been described in Japanese Patent Application 21094/80, for example, obtained by bringing benzene and 3,3,3-trifluoropropylene into reaction in the presence of hydrogen fluoride, boron trifluoride or a mixture thereof. Also the catalyst used in the afore-mentioned reaction, i.e., the reaction between (3,3,3-trifluoropropyl)benzene and benzyl chloride is carried out in the presence of a Friedel-Crafts catalyst. For example, aluminum chloride, ferric chloride, antimony pentachloride and sulfuric acid, and as a solid acid catalyst, silica-alumina and synthetic zeolite are possibly used.
The above-mentioned reaction can be carried out continuously or in batch wise under relatively mild reaction conditions of temperature and pressure. The following is an example of batch wise case.
Into a reaction vessel provided with a stirrer, a thermometer and a reflux condenser, (3,3,3-trifluoropropyl)benzene and a catalyst are introduced, and while maintaining them at a predetermined temperature, benzyl chloride is dropped into the vessel. The reaction temperature is desirably 0.degree. to 50.degree. C. when a metal chloride is used as the catalyst and 90.degree. to 150.degree. C. when a solid acid catalyst is used.
In either case, the reaction is carried out under ordinary pressure. The preferable amount of the catalyst is 0.2 to 2.0% by weight of (3,3,3-trifluoropropyl)benzene in the case of a metal chloride, and 5 to 20% by weight in the case of a solid acid catalyst. The reaction completes within one to 10 hours under the above-mentioned conditions.
After the reaction is over, the catalyst is removed from the reaction mixture by filtration or washing with water depending on the catalyst used, and then the reaction mixture is distilled to obtain phenyl-(3,3,3-trifluoropropyl)phenylmethane as a colourless and transparent liquid.
The product of the present invention, an aromatic compound substituted by trifluoropropyl has a high dielectric constant, a high insulating resistance and a low dielectric loss, and accordingly is possibly used as an insulating oil.